1. Field of the Invention
This invention concerns a Kelly Mud Saver Valve Sub for preventing loss of drilling mud from above the valve when the drill string is broken below the valve.
2. Discussion of the Prior Art
In the drilling of oil and gas wells, a drill string is lengthened by disconnecting the kelly from the drill string and inserting an additional segment of drill string between the kelly and the existing string. When the connection between the kelly and the drill string is broken, drilling mud contained within the kelly spills out onto the job site. Spillage of the drilling mud presents hazards to the safety of drilling personnel, increased expense as a result of the wasted mud, environmental pollution, and time delays occasioned by the necessity of removing workmen from the site to avoid mud spray.
To prevent spillage of the mud when the connection with the drill string is broken, mud saver valves have been developed for placement between the drill string and the kelly. These valves are designed to open when drilling mud is introduced into the drill string, but to close when the introduction of drilling mud stops. Closure of the valve retains mud in the kelly when the connection with the drill string is broken.
An example of an unsuccessful attempt to design such a valve is shown in U.S. Pat. No. 4,364,407 issued to Hilliard, which shows a mud saver valve having a tubular body with an annular seat ring mounted within the body. A closure member is axially movably mounted within the body for engagement with the seat ring. The closure member includes a bore substantially coaxially aligned with the central opening of the annular seat ring, and a flange extends radially outwardly from the closure member to slidingly engage the interior of the cylindrical body. A plug is removably mounted in the closure member with a shear ring, and the plug is movable between a first position in which the plug sealingly engages the shear ring and a second position that allows fluid to flow upwardly between the plug and the shear ring. The Hilliard device has, however, only a single seal around the flange that extends radially outwardly from the piston. Accordingly, the piston opens and closes in response to the flow of mud from the kelly into the drill string. Since most drilling operations use duplex or triplex pumps, there is a variation in the flow of drilling mud, and as the flow varies the entire valve oscillates up and down thereby causing wear on the flange, annular seat ring, and adjacent parts thereto. Hilliard also suffers from the drawback that the bore of the sub and the flange are exposed to the turbulent flow of abrasive drilling mud, and is accordingly worn down quickly in use.
U.S. Pat. No. 4,128,108 issued to Parker, et al has the same problem as Hilliard, i.e, there is only one seal at the top of the closure member so that the force of the velocity of the drilling mud holds the tool in its open position. Another problem with Parker is that the seating faces of the closure member and annular seat are flat, which provides a leak path for mud under high pressure because flat faces do not self center.
U.S. Pat. No. 3,965,980 issued to Williamson came closer to solving the problem of oscillation in the valve due to variation in flow of the mud. Williamson provided a piston body having unidirectional seals at its top and bottom, thereby forming an annular chamber around the piston body. The one way seals permit fluid to leave the annular chamber, but not enter it; the piston body then theoretically opens and closes in response to differential hydraulic force above and below the piston, thereby avoiding oscillation of the piston in response to variations of flow from duplex or triplex pumps. Williamson, however, did not provide any means for reducing the surface area of the piston against which the downhole pressure works. The Williamson valve accordingly should require higher pressures to open, is subject to closing if these higher pressures are not maintained, and still oscillates.
Accordingly, it is an object of the present invention to provide a kelly mud saver having a reciprocating closure member provided with first and second unidirectional seals which define the ends of an annular chamber around a closure member. The unidirectional seals permit fluid to leave the annular chamber but not enter it, thereby permitting the closure member to open and close in response to hydraulic force in the system instead of in response to the force of the velocity of mud flow.
It is also an object of the invention to provide such a valve with a stationary snap ring carried by the tubular valve body which surrounds the closure member. This snap ring prevents downhole pressure from being communicated to the reciprocal closure member, thereby reducing the surface area against which the downhole pressure is exerted. As a result, lower uphole pressure is required to open the closure member, and once open the closure member stays more firmly in the open position.
It is also an object of the present invention, in certain embodiments, to provide a spear assembly axially movably mounted within the closure member for venting excessive downhole pressure past the valve. In especially preferred embodiments, the spear assembly is held within the closure member by a plurality of deformable legs which permit the spear to be selectively inserted or removed from the closure member without the necessity for repairing the spear assembly in a shop.
It is also an object of the invention to provide preferred embodiments in which the body of the closure member is protected from turbulent flow of abrasive drilling mud when the valve is in an open position.